US2429849A

US2429849A - Color television system

Info

Publication number: US2429849A
Application number: US616619A
Authority: US
Inventors: Frank J Somers
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1945-09-15
Filing date: 1945-09-15
Publication date: 1947-10-28
Anticipated expiration: 1964-10-28

Description

Oct. 28, 1947.

F. .1 soMgRs COLOR TELEVIS ION SYS TEM Filed Sept. l5, 1945 2 Sheets-Sheet l @AA/k J J 0,145,652

ATTORNEY Patented Oct. 28, 1947 COLOR TELEVISION SYSTEM Frank J. Somers, Jackson Heights, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application September 15, 1945, Serial No. 616,619

25 Claims. l

Ihis invention relates to an improvement in television systems and more particularly to an improvement in the operation of transmitter components used to provide sequential color television transmissions.

In the transmission of color television images, it is conventional to break-up the image into three colors, namely red, blue and green, and image or video signals representative of each of these component colors of which the original is formed are transmitted sequentially. In order to produce signals representative of the three selected component or primary colors, optical light iilters are employed at the transmitter and these lters of appropriate red, blue and green component colors are sequentially interposed in the optical axis of the television camera or image pick-up tube. Light filters for such a purpose have -been arranged in various manner but the more usual arrangements of the filters is in the form of a lter drum or lter disc. The filters that are normally used in a color television system are Wratten filters, Nos. 25, 47 and 58 for the red, blue and green respectively.

The loss of light intensity due to the necessity of using these iilters for color separation makes it highly desirable to use a television camera or image pick-up tube having high sensitivity. For this reason, television `camera or image pick-up tubes oi the so-called storage type are generally employed. The light transmitting eiciency of the various color iilters is not identical and, furthermore, the spectral response curve of the television camera or image pick-up tube for different colors is non-panchromatic and, in fact, with present tubes, is decidedly non-linear. The spectral response of the television camera tube may be altered or controlled in accordance With the choice of the photoelectric light responsive material that is employed, but, even at best, there is considerable deviation in the response to the television camera tube insofar as the particular individual colors are concerned.

Since the light transmitting eiciency of the optica-l light path including the filters is not uniform for all component or primary colors, and since the spectral response of the television camera tube is non-linear, the output image or video signals produced by the television camera tube corresponding to the three component colors do not bear the proper relative signal strengths to produce a desired and proper color balance in the reconstructed electro-optical images produced at e, television receiver connected to receive the transmitted signals. To overcome this disadvantage and in order to produce a desired color balance at the television receiver, various circuit arrangements have been employed which. operate in one manner or another to cyclically control the degree of ampliiication to which the signals representative oi the various colors are subjected. Systems which require some form of electron switching or some form of intermittent or cyclic control of the gain of a video signal amplier have already been proposed for this purpose.

In the present invention a provision is made whereby it is possible to produce television image signals representing the various component colors which are more nearly properly related in signal strengths. This is accomplished broadly by controlling the amount of light of a particular color that is permitted to be projected upon the light responsive electrode of the television camera or image pick-up tube.

In some iconoscope television camera tubes of the storage type, the response for the red component color is materially greater than the response for the blue and green component colors. Accordingly, if color lter elements or segments of substantially uniform area are employed, the video signal output from the television camera tube would be materially greater for those signals representative of the red component than for the signals representative of the blue and green. In accordance with the present invention, the relative signal strengths of the signal representing the various component colors are made substantially proper by a choice in the size or area of the ilter elements used. In other Words, if the response of the television camera tube is much greater for the red component color, then the size or area of the red filter used at the television transmitter is reduced in order that the light responsive surface of the camera tube is exposed to an image through the red filter for a proportionately shorter length of time and accordingly a less intense electrostatic image is produced on the mosaic electrode of the television camere. tube with the result that the signal strength of the signals representative of the red component color are reduced to a value that will give substantially proper color balance at a television receiver.

Itis, therefore, one purpose of the present invention to provide in a television transmitter a series of color lters, the effective areas of which are chosen so as to produce substantially proper color balance at a television receiver.

Another purpose of the present invention resides in the provision of a plurality of lters in a television transmitter in which the sizes of the lters are so chosen as substantially to compensate for the lack of uniformity in light transmitting efficiency of the filters and the lack of linearity in the spectral response of the television camera or image pick-up tube.

A still further purpose of the present invention resides in the provision of a color lter drum or disk in a television transmitter in which the effective areas of the various filters used in the drum or disk are so chosen that substantially proper color balance will be produced at a television receiver.

Various other purposes and advantages will become more apparent to those skilled in the art from the following detailed description particularly when considered in connection with the drawings, wherein:

Figure 1 shows curves used in explaining the e operation of the present invention;

Figures 2 and 3 show a television camera or image pick-up tube and an associated color lter drum incorporating the present invention;

Figure 4 shows a development of the color filter drum shown in Figures 2 and 3; while,

Figures 5 and 6 show color lter disks incorporating the present invention for use in connection with a television transmitter.

For explaining the theory and operation of the present invention, Figure 1 shows the spectral response curve I0 of a television camera or image pick-up tube of iconoscope type. It must be pointed out that this curve, although representative of a particular light responsive electrode surface, is shown only by Way of example and that the light responsive electrode surfaces used in various other television camera or image pickup tube of storage type may, in fact, have somewhat diiferent spectral response curves. The curve Ill is plotted to show the relative sensitivity7 of the light responsive electrode or photosensitive mosaic element as a function of the Wave length of the light projected thereon where the wave length is measured in millimicrons (ma). As a matter of comparison, the response of the average human eye with respect to the spectrum is also shown in Figure 1 by curve I2. By an inspection of curve It of Figure l, it may be seen that the response of the light responsive electrode for actinic radiation having a wave length corresponding to red is materially greater than the response of that surface for radiations having a wave length corresponding to blue or green. Furthermore, it will be observed that the relative sensitivity of the electrode is not materially different insofar as the two colors blue and green are concerned, although of these two, the response of the surface of the tube referred to for one example is least for blue.

Figure 2 shows a portion of a television image pick-up or camera tube I 4 which includes a light responsive target surface I6 with which is associated a mosaic electrode element I8. The mosaic I8 is scanned by a narrow focused cathode ray beam represented by the dash-dot line 2? in order to produce video output signals. The construction of the television camera tube or the various elements contained therein form no part of the present invention and in fact, different types of television camera tubes may be used. The text Television Engineering by O. G. Frick published by McGraw-Hill Publishing Co., Inc., N. Y. in 1940, shows various types of suitable camera tubes.

Positioned in front of the television camera tube is a color lter drum 22 which carries red, green and blue

component color lters

24, 26 and 28 respectively. The color lter drum is rotated by means of a motor 3G or any other appropriate driving means. A lens system 32 is also provided for focusing the image of the objects to be televized upon the light responsive electrode I5. In order to direct the image upon the light responsive electrode, a mirror or reflecting surface 34 is positioned inside the color filter drum. This mirror or reflecting surface remains stationary as the drum is rotated and rotation of the drum causes the filters to be successively interposed in the optical axis. In order that the speed of rotation of the color filter drum may not be excessive, it is conventional to utilize more than a single one of each of the three filters and in Figures 2 and 3 it will be observed that the filters are arranged in pairs positioned diametrically with respect to the color lter drum. Since two sets of color filters are employed about the periphery of the drum the speed of rotation of the drum is reduced to one-half of the color field repetition rate.

For maintaining the filters in position, spokes are provided about the periphery of the drum for providing a rigid support means for the filters and, furthermore, these spokes cast a shadow on the light responsive electrode of the television camera tube. It is desirable that the scanning operation be carried out in the shadow of these spokes since increased video signal strength results by such operation. Production of television image signals by scanning in the shadow of the spoke is shown and described, for example, in Schade application, Serial No. 376,770, filed January 3l, 1941, and in Schade Patent No. 2,413,- O75, issued on Dec. 24, 1946.

In accordance with the present invention, the effective area or color lter signals is not uniform for all the filters, but instead their effective areas, i. e., the distance that they extend around the periphery of the lter drum is chosen as an inverse function of the light transmitting efficiency of the filters and the response of the television camera tube. It will be observed, therefore, that the width of spokes or the opaque portions between the filters is not uniform and that the peripheral dimension of the filters is similarly not uniform. The red filters 24 extend around the periphery of the filter drum by an amount substantially less than do the blue and

green filters

28 and 26 respectively. The opaque or spoke portions 36 that separate the red and blue color iilters are, therefore, materially wider than are the spokes or opaque portions 38 that separate the other color filter segments.

For a better conception of the construction of the color filter drum, a development of the drum is shown in Figure 4 and with it is associated the television camera tube I4 and the light responsive surface I6. The direction of movement of the color filters with respect to the camera tube is represented by the arrow 40. The color sequence is, therefore, red, blue and green. The areas or the relative dimensions of the lters in the direction of motion is clearly apparent from an inspection of Figure 4 and it will be observed that the blue and green filters are substantially like size or area whereas the red lters have been reduced in size (in the dimension of the direction of travel) by an amount of approximately 50 percent. The extent'ofthisreduetion, 'which may .be .from -io-to 60 percent, for example, depends upon'the spectral response curve of the. partioularglight.responsive surface employed together with lthe relative y,light transmitting eine-iene?! .ofthe rvarious lters.

- When such a filter drum isl employed, it willbe ollpalent .that thelengthof time that .the 'light responsive electrode is lexposed-to :light transmiti/ed through the Arediilter is materially less than the length o fatime that it is .exposed to light transmitted through the blue and-green filters. Accordingly, :an electrostatic v,charge image of lowerintensity `will-be producedupen the tube mosaicvelectrode `for the red image ,than would be the .case if a 4normal fullfsized filter element were employed. Since the response ofthe .teleF Vision Acaf-nera or image pick-up tube is .greatest for aetinie radiations having a wave lengthin the vicinity of the color red, then byproperly reduci-ng the-eiective size of.v the red lter element-or byproperlyproportion-ing the relative effective areas of the color filters, a series'rof television video signalsmay be produced which may-be eiective to .cause the production of. a

substantially .balanced color television limage .at

a receiver without .the necessity of inV any way altering. the relative signal strengths of. the signals representing the various colors after once they have .been generated.

The use of acolor .lterdrum such as :shown in `vFigures 2 and 3 yresults .a compact con struction and has `certainadvantages, `although such .a construction is also undesirable in certain respects. When such a nlterdr-um isemeloyed, it is necessary to utilize a Ymirror .or reiieetins surfacell -(preferably a frontsurface reflect ingmirror) which absorbs some light; and vcorrespondingly reduces .the amount of effective light that is permitted to strike the-light .responsive surface. Furthermore,:the-necessity of placing; .the lens 32 at right anglestothe light re.- sponsive surface results iny an unsymmetrical mechanical design of thev A.television f camera proper. Furthermore, by reason of `t-he relatively lon-g path or space that-interyenes between'the lens 32 and the light responsive :surface l5., .short focal lengthlen-ses cannot be readily employed. Av further objection tothe use 'of' thedrum resides-in the .fact that the Width of the shadow cast-by the spokes of the drum does'not remainv uniform over the ,entire lghtfresponsive lsurface I 5` ysince the-.distance between .the spoke vand the light responsive :surface is a function-.0i the angul-arI position of ythe drum. TheShadow cast by the spoke isonarrowest. when the spoke -is nearest the light responsiveelectrode, but Ythis shadow is 4Wider at both the top and the bottom of the light responsiveeleotrode.

All of these disadvantages maybe overcome through the use of a color ilter disc such as shown in `Figures 5 and 6.. In both of these figures the color lter discs as shown incorporate the present invention and in each case, the discs include the three .color filter yelements .arranged in sequence. The particular conguration of the color nltersegments is such that each filter progresses in as nearly a vertical direction as is possible with respect to 4the light responsive electrode of the television pick-up tube.

In Figure 5 Athe red iilter segments are shown at 52 while the blue and green filter segments are shown at 5l! and 56, respectively.V The vdirection of rotation of lter disc is -shownby the arrow 58. It will be yobserved that the width lofv the red lters 52 vis materiallyless than the width of the blue and green .filters and, 'accordingly, the spoke i 6.0 betvveenthe` red and blue iilters is wider-than-the remaining spokes of the disc. The relative 'posi/- tion of Vthe iight responsive electrode is represented by the dot-ted rectangle 62. As the disc isrotated in a clockwise direction, .the progress of the lters with respect to the light responsive electrode of the camera tube is from-bottom to top since the vertical scanning is carried out `in this direction. `This is actually from top to bottom insofar as the optical image is concerned, since the image is inverted by the optical system. Byproportionin-g the relative effective sizes of the lter elements Vof .the disc as shown inlFigure .5, for example, color television video signals willbe generated which bear the proper relative intensity with respectto the various color components so that a substantially properly balanced colorv televsionimage may be produced at a televisionre.- ceiver.

Figure 5 diifers from Figure 6 only in that the wide spoke 64 of Figure 6 occurs between the green and red lters rather than between the red and blue -l-ters as in Figure 5. It is more or less im- .1. material whether .the reduction in size is made at the ,leading or trailing edge of the filter element and, :in fact, it is possible to position the red filter segment such that substantially-equal amounts-.are removed from each side, i. esso that the spokes on adjacent sides of the red hlters are substantially of the same width but of a width greater than the spoke between the'bJme and green filter elements.

Ii .a disc such as .shown in Figure y5 is employed and if the scanning operation is carried out in the shadow of the spokes, then the light responsive electrode -will be vindarllness for a longer period of time -followingan exposure to the red v.component color image and before the scanning op eration takes place than will be the` 4casewith respect toany other color iilter. During this in terval, it is .possible that some averagingo-the .electrostatic charge might take `place although the extent of such an .action Will `besmall indeed. if it is desired- -to .eliminate any such possibility a .disc having a .construction suchas .shown in Figure 6 ycould be used since in this; instance, any particular point on'the lightresponsive electr-ode is scanned by the cathode ray beam a predetermined tirne interval after ocultation by a spoke regardless. of the width of that spoke.' After an image correspond-ing to the green component color has been scanned, there is a-time lag before the light responsive electrode is exposed to an image corresponding tothe red component color. In any respect, the configuration of the disc'shoulcl be such that the shadow produced by the spokes as the disc is rotated, travels parallel to itself from bottom to top Yacross the light responsive electrode.. This construction gives rise to a vuniform output signal as .the scanning progresses from left to right (*for each individual line) .because all areas included inthe shadowhave had the same exposure time, or, more precisely, the same charging time, under the influence of the color lter just preceding. By regulating the relative eective areas of the lters, the relative signal strengths ofY the video .signals produced for the various component colors may be so .controlled that substantially correct color balance will result in the image'produced at a television receiver.

The same result cannot be accomplished :by a change in the density of one'of the lilters while reclaiming substantially equal eiiective areas for al1 of the filters.` A change in the density of a lter alters its pass band characteristics but does not appreciably alter the amount of transmitted light in the region of maximum transmission. n color television it is desirable that certain pass band characteristics of the lters be retained in order to obtain best results and for this reason filter density changes or alterations cannot be used to accomplish proper color balance. A desired color balance of an image at a receiver can be obtained, however, by altering the relative sizes of the filters, as explained above.

I claim:

1. A color television transmitter for producing video signals representative sequentially of a plurality of diierent component colors of an object area including a television camera tube for converting optical light images into video signals, a plurality of light lter elements of different predetermined colors, means for sequentially introducing the filter elements into the optical light path of the camera tube, and means for establishing dissimilar eiective areas of the plurality of lter elements.

2. A sequential color television transmitter wherein are produced video signals representative of a plurality of different component colors of an object area including a television camera tube for converting optical light images into video signals, an optical system for the pick-up tubes, a, plurality of light lter elements of predetermined diierent colors, means for sequentially introducing the filter elements into the optical system of the camera tube, and means associated with said last named means for establishing different and dissimilar eiective areas of the plurality of lter elements.

3. A sequential color television transmitter for producing signals sequentially representative of selected component colors of an object area including a television camera tube having a light responsive electrode upon which an electrostatic charge image is produced when an optical image is projected thereon, a plurality7 of light filters including at least one of each selected component color, means sequentially to introduce the individual component color filter elements into the optical light path of the television camera tube sequentially to produce electrostatic charge ime ages individually representative of the said color components of an object area, and means for altering the effective area of one of the component color lter elements relative to other component color filter elements thereby to alter the intensity of the electrostatic charge image produced during the time interval that the said one filter element is in position in the optical light path of the camera tube.

4. A sequential color television transmitter for producing signals sequentially representative of red, blue and green component colors of an object area including a television camera tube having a light responsive electrode upon which an electrostatic charge image is produced when an optical image is projected thereon, a plurality of light iilters including red, blue and green filter elements, means sequentially to introduce the filter elements into the optical light path of the television camera tube to sequentially produce electrostatic charge images individually representative of the red, blue and green components of an object area, and means to proportion the elective area of the red filter element with respect to the other lter elements thereby to alter the intensity of the electrostatic charge image produced during the time interval that the red filter element is in position in the optical light path of the camera tube.

5. A sequential color television transmitter for producing video signals sequentially representative of the plurality of diierent component colors of an object area including a television camera tube for converting optical light images into video signals, a plurality of light iilter elements 0f different predetermined colors positioned on a rotatable color filter disc, means to rotate the disc to sequentially introduce the lter elements into the optical light path of the camera tube, and means incorporated as a part of the filter disc for modifying the effective area of the lter element of one particular color by a predetermined amount with respect to the effective areas of the other iiiter elements, whereby the sequentially produced video signals representing the component colors of the object area will bear the proper relative signal intensities to produce a substantially correctly color balanced image at a television receiver.

6. A sequential color television transmitter for producing video signals sequentially representative of the plurality of different component colors of an object area including a television camera tube for converting optical light images into video signals, a plurality of light filter elements of different predetermined colors positioned on a rotatable color lter disc, means to rotate the disc to sequentially introduce the filter elements into the optical light path of the camera tube, the eiective areas of the plurality of diiferent filter elements being so proportioned, with respect to each other, that the produced video signals sequentially representing the component colors of the object area, will be of the proper intensities relative to each other, to produce a substantially correctly color balanced image at a television receiver.

7. A sequential color television transmitter for producing video signals sequentially representative of the plurality of different component colors of an object area including a television camera tube for converting optical light images into video signals, a plurality of light lter elements of diierent predetermined colors positioned on a rotatable color filter disc, means to rotate the disc to sequentially introduce the lter elements into the optical light path of the camera tube, and means for proportioning the time intervals that the various lter element are in the light path so that the produced video signals representing the sequential component colors of an object area will bear the proper relative signal intensities to produce a substantially correctly color balanced image at a television receiver.

8. A color lter drum for use in connection with a sequential color television transmitter including a plurality of light ilter elements arranged about the periphery of the drum, the colors of the lter elements sequentially differing in a predetermined order, and means for establishing ie dimensions of the individual filter elements in the direction of rotation of the drum so that their effective areas are made unequal with respect to each other to result in the production of a substantially correctly color balanced image at a a television receiver.

9. A color filter drum for use in connection with a sequential color television transmitter including a plurality of differently colored light filter elements arranged about the periphery of the drum in substantially uniform spacing and in a predetermined order, opaque areas or spokes positioned between adjacent iilter elements. and

means for so dimensioning the spokes in the direction of rotation of the drum such that the widths of the spokes between different lter elements are dissimilar, and accordingly the corresponding dimension of the plurality of filter elements are dissimilar, with respect to each other, whereby a substantially correctly color balanced image is produced at a receiver.

10. A color filter disc for use in connection with a sequential color television transmitter comprisingr a plurality of light filters of predetermined different colors positioned on said disc, said filter elements being substantially uniformly positioned on said disc, and means for pro-portioning the dimensions of the plurality of filter elements of different colors so that their effective areas are unequal, with respect to each other, thereby to compensate for unequal color response of the television transmitter.

11. A color filter disc for use in connection with a sequential color television transmitter comprising a plurality of spirally shaped light opaque spoke members, a plurality of different light filters of substantially spiral shape positioned between the spokes, said light filters being of different colors and arranged in a predetermined order, and means whereby the widths of the spiral opaque spokes are dissimilar so that the effective areas of the differently colored light filter elements are unlike with respect to each other.

12. A color lter disc for use in connection with a sequential colo-r television transmitter comprising a plurality of spirally shaped opaque spoke members, a plurality of different light filters of substantially spiral shape positioned between the spokes, said light filters being of different colors and arranged in a predetermined' order, and means for establishing the widths of the various opaque spokes and the effective areas ofthe differently colored filter elements so that they are unlike with respect to each other.

13. A color filter assembly for use in connection with sequential color television transmitter including a plurality of light lters of different colors arranged in a predetermined order with an opaque areaintermediate each of the lter elements, said filter elements being arranged in substantially uniform displacement on said assembly, and means for establishing a non-uniform ratio of the size of the opaque portions to the adjacent filter elements.

14. A filter assembly for use in connection with a sequential color television transmitter including red, blue and green lter elements arranged in a predetermined order, opaque portions intermediate each of the adjacent filter elements, and means whereby the effective area of a filter element of one particular color is reduced by a predetermined amount over the effective areas of the filter areas of the lter elements of the other colors by an increase in the area of the opaque portion immediately adjacent the filter 17. A movable color separator filter unit for presenting sequentially changing color versions of an optical image sequentially shifting from one color to another at a predetermined rate and through which images are directed along a predetermined optical path toward a light responsive surface, comprising a support unit having thereon a plurality of light transmitting filters each of a selected component color, each of said filters having an area of such size relative to each other area that the light passed therethrough to the light responsive surface in a selected unit time period substantially coinciding with the sequential shift from one color to another is such that the surface response to each component color of light is substantially uniform.

18. A movable color separator filter unit for presenting sequentially changing color versions `of an optical image and through which images are directed upon a light responsive electrode along a predetermined optical path across which path the filter unit is arranged to move at a substantially uniform rate, comprising a support member having thereon a plurality of light transmitting filters of different selected component colors, each of said filters having an area of such size relative t0 each other area that the light passed therethrough to the light responsive surface is such that the surface response to each component color of light is substantially uniform.

19. A movable color separator lter unit for presenting sequentially changing color versions of an optical image and through which images are directed along a predetermined optical path toward a light responsive surface across which path the filter unit is arranged to move at a substantially uniform rate, comprising a support assembly having thereon a plurality of light transmitting lters of different selected component colors, each of said lters having an area of such size relative to each other area that the light passed therethrough to the light responsive surface during the time that each is in the light path is such as will produce substantially uniform response at the light responsive surface for each component color.

20. The method of operating a sequential color television transmitter in which a television carnera tube having a light responsive electrode is employed for converting an optical image into an electrostatic charge image and in which a plurality of light filters in the optical light path of the camera tube to produce electrostatic charge images representative of the different component colors of an object area, and dimensioning the effective areas of each of the plurality of filters relative to each other sothat they are dissimilar by predetermined amountsthereby to alter the relative time intervals during which the light responsive electrode is exposed to light transmitted through the said filters.

21. The method of operating a sequential color television transmitter in which a television camera tube having a light responsive electrode is employed for converting an optical image into an electrostatic charge image and in which a plurality of light filters of predetermined different colors are provided which comprises the steps of sequentially introducing the light filters in the optical light path of the camera tube to sequentially produce charge images representative of the color content of an object area for the different filters used, and selecting the effective areas of the plurality of lters so that they are dissimilar by predetermined amounts.

22. The method of operating a squential color television transmitter in which a television camera tube having a light responsive electrode is employed for converting an optical image into an electrostatic charge image and in which a plurality of light lters of predetermined component colors are provided which comprises the steps of sequentially introducing the light filters in the optical light path of the camera tube to sequentially produce charge images representative of the different component colors of an object area, and selecting different relative time intervals that the light responsive electrode is exposed to an optical image transmitted through the various different lters.

23. The method of operating a sequential color television transmitter in which a television camera tube is employed for converting optical light images into a series of video signals and in which a plurality of light lters of different predetermined colors are provided which comprises the steps of sequentially positioning the light lters in the optical light path of the television camera tube, directing light from an object area through the filters as they are sequentially interposed in the light path so that Video signals are produced corresponding sequentially to the predetermined colors of the object area, and selecting the duration of time that a iilter of a particular color is interposed in the light path with respect to the duration of time for the other filters whereby the relative intensity of the video signals representing the one particular color will be altered with respect to the intensity of the signals representing the other Component colors.

24. The method of operating a sequential color television transmitter in which a television camera tube is employed for converting optical light images into a series of video signals and in which a plurality of light lters of different component colors are provided which comprises the steps of sequentially positioning the light filters in the optical light path of the television camera tube directing light from an object area through the filters as they are sequentially interposed in the light path so that video signals are produced corresponding sequentially to the component colors of the object area, and determining the duration of time that a lter of a particular color is interposed in the light path with respect to the duration of time for the other lters whereby the relative intensities of the video signals representing the different component colors of the object area will be such that a substantially properly balanced color image will be produced at a receiver. 25. The method of operating a sequential color television transmitter in which a television camera tube is employed for converting optical light images into a series of video signals and in which a plurality of light lters of different component colors are provided Which comprises the steps of sequentially positioning the light lters in the optical light path of the television camera tube directing light from an object area through the filters as they are sequentially interposed in the light path so that video signals are produced corresponding seqnentially to the component colors of the object area, and selecting different durations of time that the different light lters are interposed in the light path whereby the relative intensity of the video signals representing the different component colors will be altered.

FRANK J. SOMERS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,193,722 Hardy Mar. 12, 1940 2,378,746 Beers June 19, 1945